The invention is a polyelectrolyte solid system, a method for its production and a wound dressing.
Based on their high content of covalently bonded salt groups, polyelectrolytes (PTE) possess the ability to absorb large quantities of water and in so doing to go into solution. In many applications, particularly in the area of treating wounds, pediatric care and incontinence materials, where it is a matter of binding secreted water, or aqueous secretions, it is necessary to maintain the integrity of the absorber used so that it can be removed in a mechanically stable form. To ensure this, the otherwise water-soluble polyelectrolytes are crosslinked in many different ways by means of intermediate bonds, by covalent or ionic bonds to the extent that, upon the entry of water, solvation occurs only to the stage of highly swollen gels.
Since absorbers of this kind on a polyelectrolyte base are hard and brittle because of their high salt content and their crosslinking in the solid state, they are embedded in flexible polymers, specifically in cellulose or in polyurethane, in order to obtain good workability and to fixate them against being flushed out.
This is the description given by the Beiersdorf Company to a polyurethane foam under the commercial name “Cultinova”, in which extremely fine superabsorbent particles of partially crosslinked polyelectrolyte powders are dispersed.
This flexible material, when introduced into a physiological sodium chloride solution, is able to absorb substantial quantities of water and to act as an absorbent coating for moist wound management.
Furthermore it is known, using the viscose method, to process Na-carboxymethyl cellulose as a polyelectrolyte (PEL) together with cellulose into highly swellable viscose fibers. The fixation of the intrinsically water-soluble Na-carboxymethyl cellulose in the viscose fibers is achieved by the formation of non-water-soluble intermolecular hydrogen bridge bonds between the macromolecules of the cellulose and those of the Na-carboxymethyl cellulose. The disadvantage here is that the polyelectrolytes have to be embedded in a second flexible polymer.
Furthermore a process is described in EP 0 616 630 in which highly swellable filaments containing polyelectrolytes can be produced expensively and therefore disadvantageously by partial chemical conversion of cellulose fibers, specifically of lycoell fibers.
Ionically crosslinked polyelectrolytes, specifically ionically highly crosslinked polyelectrolyte complexes, also known as polyanion-polycation complexes, have been used only to a small extent until now for the production of absorbent materials, in spite of their easy accessibility. Polyelectrolyte complexes result from the reaction of anionic and cationic macromolecules (polyelectrolytes) and are crosslinked to each other ionically through a plurality of salt groups. They are soluble in complex systems of solutions, specifically saline solutions (JP 49099651), formic acid (JP 62183768) or water/HCl/dioxane (JP 49010232). Membranes can be produced from these solutions which, as described in U.S. Pat. No. 3,546,142 and U.S. Pat. No. 3,549,016, are suitable for ultrafiltration in aqueous solutions. The macromolecules are arranged without structure in an indifferent random orientation in these polyelectrolyte complex membranes.
In contrast, the polyelectrolyte complex membranes which, according to DD 160 393 and DD 218 734/A4, are created on the contact surfaces of solutions of anionic and cationic polyelectrolytes are distinguished by an advantageous bi-layer structure. However, these polyelectrolyte complex membranes are very thin and consequently cannot sustain mechanical loads. They are proposed primarily for encapsulating biologically active materials (DD 215 795 A1), in addition to ultrafiltration (DD 200 471/3; DD 152 287).
DE 197 41 063 describes planar entities in the form of paper, nonwoven material, woven material or laminate, which are produced from a mixture of fine fibers which are soluble in water or highly swellable anionic and cationic polyelectrolyte fibers and/or fibrins and/or spherical particles. The final structure of these materials does not form unit after water or aqueous solutions and/or aqueous emulsions and/or aqueous suspensions have acted on them through the polyelectrolyte complex membranes resulting on the contact surfaces between the polyanionic and polycationic components. The disadvantage here is that the oppositely charged fibers, fibrins or spherical particles are only ionically crosslinked at points and on the surface and consequently the resulting gel demonstrates inadequate mechanical stability.
Furthermore, in the last two decades great progress has been made in the treatment of dermal wounds, such as burns, operating wounds, ulcers. The so-called “hydroactive wound dressings” have become increasingly important. These dressings make it possible to keep the wounds moist and at the same time to absorb excess secretions, to inhibit the entry of external bacteria and to perform a non-traumatic change of the dressing because they do not adhere to the wound.
For the initial phases of healing, when cleaning is performed and secretions are present, wound coatings of this type are generally desirable, which can be conformed to the base of the wound, or easily tamponed into deeper wounds, which possess high secretion absorption capability by forming a gel and in the swollen state have adequate consistency so that they can be removed from the wound in a single or a few pieces. In later phases of healing, wound coverings which release moisture to the wound and prevent it from drying out are often beneficial.
The greatest importance in practice today attaches to applications based on hydrocolloids, hydrogels and fiber dressings from aligns.
Hydrocolloid compounds are compounds in which hydrocolloids (water-absorbent particles or polymers based on polyelectrolytes) are dispersed in an elastomer matrix. They possess great absorbency for secretions and are self-adhesive. The disadvantage is their lack of suitability for tamponage into deeper or jagged wounds, as well as their tendency to partially disintegrate under high absorption of secretions, thus increasing the time spent cleaning when changing dressings. Their application in the case of infected wounds is problematic because of the semi-occlusivity of the dressings.
The use of hydrogels as wound dressings is restricted to wounds with medium or low rates of secretion as a result of their restricted capacity to absorb secretions. Many of the gels are characterized by severe liquefaction so that they have to be removed from the wound by intensive rinsing when the dressing is changed.
These materials satisfy the performance criteria described above only to a limited extent, since they either lose their stability under heavy absorption of secretions or liquify, tamponment is difficult and they find only restricted use in the case of infected wounds.